This invention relates to a solid state color imaging apparatus utilizing a charge transfer device such as a CCD (Charge Coupled Device) and a BBD (Bucket Brigade Device) or a photodiode array and, more particularly, to such apparatus which senses and stores charges in proportion to incident light and provides a sequential color signal.
As is well known, it is preferable to use a solid state area imaging device for a television camera in place of a pick up tube for converting an optical image of an object to an electrical signal because of its long life, stability, lower power consumption, etc. Some such devices have been sold in the market.
A solid state color imaging apparatus for producing a color signal can be constructed with dichromic mirrors and three solid state imaging devices which produce three independent color component signals. However, unlike a television camera utilizing three pick up tubes, such an imaging apparatus requires much more accuracy in locating each imaging device because of the self scanning mechanism of the device. As a matter of fact three color signals from these pick up means should exactly coincide with each other to produce the color signals. Adjusting these scanning areas is easily accomplished in the tube type color camera, because the scanning area of each pick up tube is controlled properly by applying a DC current to the deflection coil of the pick-up tube. On the other hand, in a solid state imaging apparatus, the scanning area is not controlled but is determined only by the location and the size of the photosensitive area of the device. A color imaging apparatus utilizing a single imaging device does not require such accurate location of a plurality of devices.
Such a color imaging apparatus with a single solid state imaging device can be constructed by any kind of solid state area imaging device by additionally providing a striped color filter which consists of a plurality of sets of three different color transmissivity filter strips and a color signal recovering circuitry. The color filter is placed on the photosensitive area of the imaging device so that the side by side direction of the filter strips is identical with that of the horizontal scan and each filter strip covers one photosensitive element in the direction of the horizontal scan. In this apparatus, a dot sequential color representing signal is derived from the imaging device with successive horizontal scanning. Then, red, blue and green component signals are obtained from the dot sequential signal through a sampling circuit which operates in synchronism with the high speed horizontal clock and separates these color component signals from each other. The color component signals are processed to produce the color signal. The color signal can be produced by a synchronous detection method as well, namely, color difference signals are obtained through a synchronous detection circuit from the dot sequential color signal with a reference signal produced from the horizontal clock pulse of the imaging device.
In these color imaging apparatuses, however, it is necessary to provide three times the number of photosensitive elements as in a black and white imaging apparatus in order to obtain the same resolution. Therefore the size of the image pick up device also becomes three times as large as a black and white imaging apparatus. Moreover, as is well-known, many difficulties are involved in manufacturing such a large area imaging device.